1. Field of the Invention
The present invention relates to a lens system and apparatus, particularly to a lens system in which zoom and focus of a lens apparatus that is mounted on a TV camera are controlled by a controller connected with the lens apparatus, and a lens apparatus having a view angle correction function to correct, by means of a zoom lens, change of a view angle at the time of focusing.
2. Description of Related Art
A lens apparatus to be mounted on a TV camera is connected with an external controller via a cable, and each optical member such as a zoom lens and a focus lens, which are arranged in the lens apparatus, is driven by a motor. In a lens system in which the lens apparatus is controlled with the external controller, the zoom lens is controlled in general by a rate control signal, which instructs a moving rate of the zoom lens. For example, a controller (a zoom controller) used for controlling the zoom lens is provided with a rotatable operation member called a thumb ring, and when the operator rotates the thumb ring, a rate control signal for instructing a zoom rate corresponding with an operation amount is transmitted to a control part of the lens apparatus, and the control part of the lens apparatus drives the zoom lens with the motor at the zoom rate that is instructed with the rate control signal.
A lens system is conventionally known that can control positions based on a shot function, a limit function or a view angle correction function, in addition to a function in a manual control in accordance with an operation of the operation member by the operator.
In the shot function, when a shot switch, which is provided to the zoom controller, is turned ON, the zoom lens moves to a shot position that is designated by a shot position adjusting knob. The shot function is conventionally controlled in the zoom controller (e.g. Japanese patent application Laid-open No. 8-334674). The zoom controller having the shot function is called a shot box. As the shot switch is turned ON, the zoom controller obtains a current position of the zoom lens from the lens apparatus, and transmits to the control part of the lens apparatus the rate control signal for instructing a moving rate in a moving direction so that a difference between the current position of the zoom lens and the designated shot position approaches zero, the moving rate corresponding with the difference. Thus, the control part of the lens apparatus drives the zoom lens in accordance with the rate control signal, and the zoom lens thereby moves to the shot position.
In the limit function, when a limit switch, which is provided to a controller, is turned ON, a moving range of the zoom lens is restricted within a range of a limit position. The limit function is conventionally controlled in the controller like the shot function (e.g. Japanese patent application Laid-open No. 10-39193). The current position of the zoom lens is obtained from the lens apparatus in the controller while the operation member of the controller is being operated, and when the current position of the zoom lens moves in a direction to approach the limit position, the rate control signal transmitted from the controller to the control part of the lens apparatus is restricted at a rate corresponding with the difference between the current position of the zoom lens and the limit position. If the current position of the zoom lens exceeds the limit position, the rate control signal for returning the zoom lens to the limit position is transmitted to the control part of the lens apparatus. Therefore, the control part of the lens apparatus restricts the moving range of the zoom lens to be within the limit position by driving the zoom lens in accordance with the rate control signal provided from the controller, without recognizing the limit position.
In the view angle correction function, the change of the view angle due to the moving of the focus lens is prevented by moving the zoom lens. The view angle correction function is conventionally controlled in the lens apparatus (e.g. Japanese patent application Laid-open No. 10-282396). The control part of the lens apparatus moves the zoom lens by its control at a position where the view angle is constant when moving the focus lens. When the focus lens moves in accordance with the control signal from the controller, the control part of the lens apparatus simultaneously drives the zoom lens and the focus lens so that the current position of the zoom lens and the zoom position which makes the view angle constant correspond with each other; thereby the change of the view angle at the focus adjustment is prevented.
In the conventional art, however, the lens apparatus cannot activate the view angle correction function in a case where the shot function and/or the limit function are executed. That is, when the control part of the lens apparatus moves the zoom lens by the control based on the view angle correction function while the zoom lens moves to and stops at the shot position or the limit position by the control based on the shot function or the limit function of the controller, the controller recognizes that the position of the zoom lens is displaced from the shot position, or, in some cases, recognized that the position of the zoom lens exceeded the limit position. Then, the controller transmits the rate control signal for returning the position of the zoom lens at the shot position or the limit position to the control part of the lens apparatus. The thus transmitted rate control signal cannot be determined by the control part of the lens apparatus whether the signal is based on the shot function or the limit function, or the operation of the operation member; moreover, the zoom lens must be controlled in accordance with the rate control signal because the control based on the operation of the operating member should take the first priority; thus the zoom lens is returned at the shot position after all, and the view angle correction function does not effectively function.
Similar problems occurs not only at the time of the shot function or the limit function, but also in a state where the zoom lens moves to and stops at a target position in the position control by some function of the position control in the controller.
In the limit function, it is usually not desired to perform the view angle correction up to the level where the zoom lens exceeds the limit position; however, in the shot function, it is more often desired to perform the view angle correction function first so as to correct the view angle from the shot position also, in a case where the zoom lens moves to and stops at the shot position.
In consideration of the above-described necessity, a method has been suggested in which the control signal provided from the zoom controller is invalidated while executing the view angle correction. Yet, this method also invalidates the restriction of the limit position originally provided from the zoom controller, and thus the zoom lens can move to the outside of the limit position by the view angle correction.
Further, even though it is considered preferable to prioritize the shot function or the limit function over the view angle correction function, the zoom lens does not move effectively at the proximity of the shot position or the limit position because of a control problem under a state where the plurality of controls based on the plurality of functions are simultaneously performed.
In the conventional art, the problem presented above occurs due to the fact that plural controls based on the shot function, the limit function, view angle correction function, and so forth, are executed by the control part of the lens apparatus and by the controller that are completely independent of each other.